This invention relates to improvements in fluid flow control devices, and in particular to carburetors and float or diaphragm actuated flow control valves for controlling either fuel, vapor, or air passages. The invention further relates to a solution to the problem of undesirable leakage past a valve such as a float type fuel inlet valve or an air or vapor vent valve.
The control valves conventionally comprise a conically shaped valve member cooperating with an edge zone of a wall defining a fluid passage or orifice as a valve seat. The valve member usually is associated with a suitable float mechanism or other means for regulating or controlling the relative position of the valve member in relation to the valve seat to control fluid flow from a supply into the receptacle of the carburetor as the fuel therein is delivered into the cylinders of an engine together with the requisite amount of air to provide a combustible mixture. In some applications, both the valve and valve seat member are formed of metal such as brass or other suitable metal.
Fluid control valves having such metal-to-metal contact between the valve member and valve seat encounter problems due to the presence of minute dirt particles in engine fuels which may hold the valve member open when it should be closed thereby permitting leakage of a portion of the fuel past the valve seat and through the port to the fuel bowl. This leakage results in excess consumption of fuel and also may be sufficient to raise the fuel level or pressure in the carburetor bowl and cause flooding of the carburetor and enriched air-fuel mixture or charge to the engine thereby producing stalling and/or subsequent difficult starting of the engine. Moreover, the repeated metal-to-metal contact during the opening and closing action in the fuel control valve during the use of the carburetor causes wear of the valve seat and valve. The high frequency engine vibration also aggravates wear of the metallic valve members reducing the efficiency of the control valve.
A solution to the metal-to-metal contact problem in control valves described above which has been proposed involves the use of a valve having a flexible tip of rubber-like material working with a metal seat or, alternatively, a metal needle valve working with a rubber valve seat. Examples of patents describing needle valves with resilient tips include U.S. Pat. Nos. 3,236,496; 3,090,596; 3,445,089; 2,414,577; 3,531,086 and 3,326,520. Most of these patents describe various configurations for flexible tips of rubber-like material, which tips may be comprised essentially of rubber or may be a metallic tip to which the rubber is molded and locked in place. Examples of prior art patents describing the use of valve seat constructions wherein the valve seat is formed of a yieldable or resilient rubbery material and cooperates with a metallic valve member include U.S. Pat. Nos. 2,953,347 and 3,236,496. As mentioned above, these patents suggest the use of such flexible materials for the purpose of overcoming leakage of fuel in cases of wear, engine vibration or misalignment of the valve structure in use.
The rubber-like resilient materials which have been suggested as being useful as the tip of the valve member or as the valve seat have included such rubber materials as neoprene (polychloroprene), thiorubbers, nylon and Buna-N (butadiene acrylonitrile) although the utility of such rubbers for valve tips in contact with highly aromatic fuels is questioned in U.S. Pat. No. 3,236,496.
It is essential that the rubber-like material utilized in the flow control valves be resistant to the fuel passing through the control valve. In the presence of gasolines and fuels of high aromatic character, and under the operative temperature conditions to which carburetors are conventionally subjected, such as, for example, temperatures in the order of 210.degree.-220.degree. F., the synthetic rubber tips and valve parts may become soft and pudgy and stick to the metallic parts of the control valve. Alternatively, the rubber-like material may swell to such an extent as to upset the fuel control characteristics of the carburetor and change the flow rate to the carburetor bowl. Similar flow rate changes may occur due to heat or compression set or due to volume changes in the rubber-like parts resulting from the ultimate wetting of these parts with the fuel at the operating temperatures and subsequent drying thereof in ambient temperatures when the carburetor is not functioning.
A solution to the problems resulting from the use of the rubber-like material of the prior art described above has been proposed in U.S. Pat. No. 3,236,496 wherein there is described the use of a soft molded and cured fluoroelastomeric type material commercially available under the trade names "Viton" and "Fluorel". "Viton" is made by the E. I. du Pont de Nemours and Company and "Fluorel" is produced by Minnesota Mining and Manufacturing Co. More specifically, U.S. Pat. No. 3,236,496 describes the use of a composition wherein the elastomeric constituent consists essentially of a polymeric compound of hexafluoropropylene and vinylidene fluoride such as a copolymer containing 30% to 60% by weight of hexafluoropropylene and 70% to 40% by weight of vinylidene fluoride monomer or a terpolymer thereof with tetrafluoroethylene. These fluorinated polymers are reported to be especially useful for forming valve seats and valves which come in contact with gasoline, and it is reported that such fluorinated polymer compounds are superior for such use when compared to other cured rubbery materials such as thiorubber, Buna-N rubber, neoprene rubber, etc.
Fluid control valve tips which have been utilized in internal combustion engines in the past few years have incorporated the use of the synthetic fluorinated rubbers commercially available under the trade designations "Viton" and "Fluorel". However, this material is more expensive than other rubber-type materials and some difficulties have been observed when the material is utilized for valve tips for carburetors of high compression engines in which highly aromatic fuels are employed. The "Viton" and similar fluorinated polymers have a greater tendency to swell in the highly aromatic fuels.
Another proposed solution to the problems resulting from the swelling and drying of the rubber materials is to reduce the amount of rubber utilized on the valve tip. It has been proposed, for example, that the swelling problems can be reduced if the amount of rubber utilized in the preparation of a tip is reduced. Thus, it has been suggested that needle valves be prepared with metallic tips which may then be coated with a thin layer of rubber. Various metal tip shapes have been proposed in, for example, U.S. Pat. Nos. 3,326,520, 3,445,089 and 3,531,086 to permit the molding of a thin rubber coating with good bonding characteristics.